R3710 datasheet(10/18 Pages) ONSEMI

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RHYTHM R3710

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This tool can also be easily incorporated into another

software application.

If the noise is injected before the VC and the audio path

is also enabled, the device can be set up to either have both

the audio path and noise adjust via the VC or to have the

noise only adjust via the VC. If the noise in injected after the

VC, it is not affected by VC changes (see Table 4).

Table 4. NOISE INJECTION EFFECT ON VC

Noise

Insertion

Modes

VC Controls

Noise

Injected

Audio

Enabled

Off

Audio

Off

Yes

Pre VC

Audio + Noise

Pre VC

Yes

Post VC

Audio

Post VC

Yes

Noise only

Pre VC

Noise

Pre VC

Noise only

Post VC

−

Post VC

Pre VC with

Noise

Pre VC

Yes

Narrow−band Tone and Noise Stimulus

R3710 is capable of producing Narrow−band Noise and

Tone Stimuli that can be used for in situ audiometry. Each

narrow−band noise is centred on an audiometric frequency.

The duration of the stimuli is adjustable and the level of the

stimuli are individually adjustable.

A/D and D/A Converters

The system’s A/D converter is a second order sigma−delta

modulator operating at a 2.048 MHz sample rate. The

system’s audio input is pre−conditioned with antialias

filtering and a programmable gain pre−amplifier. This

analog output is over−sampled and modulated to produce a

1−bit Pulse Density Modulated (PDM) data stream. The

digital PDM data is then decimated down to Pulse−Code

Modulated (PCM) digital words at the system sampling rate

of 32 kHz.

The D/A is comprised of a digital, third order sigma−delta

modulator and an H−bridge. The modulator accepts PCM

audio data from the DSP path and converts it into a 64−times

or 128−times over−sampled, 1−bit PDM data stream, which

is then supplied to the H−bridge. The H−bridge is a

specialized CMOS output driver used to convert the 1−bit

data stream into a low−impedance, differential output

voltage waveform suitable for driving zero−biased hearing

aid receivers.

HRX Head Room Expander

R3710 has an enhanced Head Room Extension (HRX)

circuit that increases the input dynamic range of R3710

without any audible artifacts. This is accomplished by

dynamically adjusting the pre−amplifier’s gain and the

post−A/D attenuation depending on the input level.

Channel Processing

Figure 6 represents the I/O characteristic of independent

AGC channel processing. The I/O curve can be divided into

the following main regions:

• Low input level expansion (squelch) region

• Low input level linear region

• Compression region

• High input level linear region (return to linear)

Figure 6. Independent Channel I/O Curve Flexibility

−100

−90

−80

−70

−60

−50

−40

−30

−20

−10

−120 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20

INPUT LEVEL (dBV)

Low Level

Gain

Compression

Ratio

High Level

Gain

Squelch

Threshold

Lower

Threshold

Upper

Threshold

The I/O characteristic of the channel processing can be

adjusted in the following ways:

• Squelch threshold (SQUELCHTH)

• Low level gain (LLGAIN)

• Lower threshold (LTH)

• High level gain (HLGAIN)

• Upper threshold (UTH)

• Compression ratio (CR)

To ensure that the I/O characteristics are continuous, it is

necessary to limit adjustment to a maximum of four of the

last five parameters. During Parameter Map creation, it is

necessary to select four parameters as user adjustable, or

fixed, and to allow one parameter to be calculated.

The squelch region within each channel implements a low

level noise reduction scheme (1:2 or 1:3 expansion ratio) for

listener comfort. This scheme operates in quiet listening

environments (programmable threshold) to reduce the gain

at very low levels. When the Squelch and AFC are both

enabled it is highly recommended that the Squelch be turned

on in all channels and that the Squelch thresholds be set

above the microphone noise floor (see Adaptive Feedback

Canceller).

The number of compression channels is programmable in

ARKonline® and can be 1, 2, 4, 6 or 8.

Graphic Equalizer

R3710 has a 16−band graphic equalizer. The bands are

spaced linearly at 500 Hz intervals, except for the first and

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